Strip anonymous blocks when change in style removes need for them

LayoutTests/fast/repaint/position-change-keeping-geometry.html

Index: LayoutTests/fast/repaint/position-change-keeping-geometry.html
diff --git a/LayoutTests/fast/repaint/position-change-keeping-geometry.html b/LayoutTests/fast/repaint/position-change-keeping-geometry.html
index 8901d457e87c11e8bae2c9588092ce9b25dee07d..f65a25e76d06566eb76d1cf740be1eb3a26026bf 100644
--- a/LayoutTests/fast/repaint/position-change-keeping-geometry.html
+++ b/LayoutTests/fast/repaint/position-change-keeping-geometry.html
@@ -28,6 +28,10 @@ div {
   top: 20px;
   background-color: blue;
 }
+#target0 {
+  left: 20px;
+  position: relative;
+}
 #target1 {
   left: 20px;
   position: relative;
@@ -44,6 +48,8 @@ div {
 }
 </style>
 There should be no invalildations on change of position without actual change of position and size.
+<!-- target0 ensures we don't strip anonymous wrappers (and trigger a layout) when the other elements change position. -->
+<div id="target0"></div>
 <div id="target1"></div>
 <div id="target2"></div>
 <div id="target3"></div>